Dual spring clip attachment mechanism for controlled pressure interface thermal solution on processor cartridges

ABSTRACT

An electronic cartridge that includes a pair of spring clips which attach a thermal element to an integrated circuit or an integrated circuit package. The integrated circuit/package is mounted to a substrate. The substrate may be a printed circuit board. The cartridge may have a plurality of pins that extend from the thermal element and through the substrate. Each spring clip may have a pair of bent portions that are attached to the pins of the thermal element. The spring clip exerts a pull force that pulls the thermal element into the integrated circuit/package. The bent ports can be deflected so that at least a minimum pull force is always exerted onto the thermal element even with dimensional variations in the parts of the cartridge. The bent portions can therefore accommodate for tolerances in the cartridge while clamping the thermal element to the integrated circuit/package.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and is a continuation ofapplication Ser. No. 09/024,539, filed Feb. 17, 1998, now issued as U.S.Pat. No. 6,046,905 which is a Continuation-in-Part application ofapplication Ser. No. 08/723,027, filed Sep. 30, 1996, now issued as U.S.Pat. No. 5,838,542.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a spring clip that couples a thermalelement to an integrated circuit or integrated circuit package.

2. Background Information

Integrated circuits are assembled into packages that are soldered toprinted circuit boards. The integrated circuits generate heat which mustbe removed to insure that the junction temperatures of the circuitsoperate below threshold levels. The heat generated by each integratedcircuit primarily flows through the package. The package is typicallyconstructed from a dielectric material which has a relatively lowcoefficient of thermal conductivity. The low thermal coefficientincreases the temperature drop across the package and the junctiontemperature of the circuit.

Some packages contain a metal lid that reduces the thermal impedancebetween the integrated circuit and the ambient. A heat sink may becoupled to the metal lid to further improve the thermal efficiency ofthe assembly.

The surface roughness and a lack of co-planarity between the metal lidand the heat sink may create air gaps within the metal lid/heat sinkinterface. The air gaps increase the thermal impedance between the metallid and the heat sink. The increase in thermal impedance may raise thejunction temperature of the integrated circuit.

Some assemblies utilize a fastener such as a clip or a screw that pullsthe heat sink into the metal lid. The pull force of the fastenerdecreases the thermal impedance of the metal lid/heat sink interface.Variations in the height of the integrated circuit package due tomanufacturing tolerances may change the pull force of the fastener. Thetolerances may create an undesirable reduction in the pull force and anincrease in the thermal impedance of the metal lid/heat sink interface.It would be desirable to provide a clamping fastener for an electronicassembly which accommodates tolerances in the assembly.

SUMMARY OF THE INVENTION

One embodiment of the present invention is an electronic cartridge thatincludes a spring clip which attaches a thermal element to an integratedcircuit or an integrated circuit package. The integrated circuit/packageis mounted to a substrate. The cartridge may have a pin that extendsfrom the thermal element and through the substrate. The spring clip isattached to the pin of the thermal element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of an embodiment of an electronic cartridgeof the present invention;

FIG. 2 is a top cross-sectional view of the cartridge;

FIG. 3 is a side view of a pin of the cartridge;

FIG. 4 is a side view of another pin of the cartridge;

FIG. 5 is a top view of an alternate embodiment of the cartridge.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention is an electronic cartridge thatincludes a pair of spring clips which attach a thermal element to anintegrated circuit or an integrated circuit package. The integratedcircuit or integrated circuit package is mounted to a substrate. Thesubstrate may be a printed circuit board. The cartridge may have aplurality of pins that extend from the thermal element and through thesubstrate. Each spring clip may have a pair of bent portions that areattached to the pins of the thermal element. The spring clip exerts apull force that pulls the thermal element into the integratedcircuit/package. The bent ports can be deflected so that at least aminimum pull force is always exerted onto the thermal element even withdimensional variations in the parts of the cartridge. The bent portionscan therefore accommodate for tolerances in the cartridge while clampingthe thermal element to the integrated circuit/package.

Referring to the drawings more particularly by reference numbers, FIGS.1 and 2 show one embodiment of an electronic cartridge 10 of the presentinvention. The cartridge 10 may include an integrated circuit package 12that is mounted to a substrate 14. The cartridge 10 may contain a numberof integrated circuit packages 12 that are mounted to both sides of thesubstrate 14.

The substrate 14 may be a printed circuit board which containselectrical pads, visa and routing traces (not shown) as is known in theart. One edge of the substrate 14 may contain a plurality of conductivepads 16 that can be inserted into a card edge electrical connector (notshown). The card edge electrical connector is typically mounted to amotherboard (not shown) of a computer system.

The integrated circuit package 12 may contain one or more integratedcircuits 18 and a metal lid 20. The integrated circuit 18 generates heatthat may primarily flow into the metal lid 20. The package 12 mayfurther have solder balls 22 that are attached to the substrate 14.Although solder balls 22 are shown and described, it is to be understoodthat other contacts such as pins may be employed in the presentinvention.

The cartridge 10 may have a thermal element 24 that is coupled to theintegrated circuit package 12. The cartridge 10 may further have aplurality of first pins 26 that extend through clearance holes 28 in thesubstrate 14. The thermal element 24 may be a plate that is constructedfrom a thermally conductive material such as aluminum or copper. Thepins 26 may be screwed or pressed into the plate. A finned heat sink 30may be attached to the thermal element 24. Although a thermal plate 24that is separate from the heat sink 30 is shown in described, it is tobe understood that the thermal element 24 may include an integral finnedheat sink.

The cartridge 10 may have a pair of spring clips 32 that are attached tothe pins 26. The spring clips 32 secure the thermal element 24 to thesubstrate 14; Each spring clip 32 may have a pair of slots 34. Each pin26 is inserted through a corresponding slot 34 of each clip 32. The pins26 may each have a groove 36 that receives opposing edges of the clip32. The edges reside in the grooves 36 and prevent the pins 26 frombeing pulled out of the slots 34.

Each slot 34 is located in a bent portion 38 of a spring 32. Whenassembled to the pin 26, the bent portions 38 are deflected to exert apull force which pulls the thermal element 24 into the integratedcircuit package 12. The pull force reduces the thermal impedance betweenthe thermal element 24 and the integrated circuit package 12. A thermalgrease 40 may be inserted in between the thermal element 24 and themetal lid 20 to further minimize the thermal impedance between the twocomponents.

Variations in the dimensions of the cartridge parts may vary thedeflection of the bent portions 38 and the pull force on the thermalelement 24. The cartridge 10 is preferably designed so that the bentportions 38 are always deflected to provide at least a minimum pullforce on the thermal element 24.

FIG. 3 shows an embodiment of a pin 26. The pin 26 may have a studportion 42 that extends from a shoulder 44. The stud portion 42 isinserted into a corresponding hole of the thermal element 24. The pin 26may have a plastic bushing 45 that is pressed onto the stud portion 42and pressed into the thermal element 24. The shoulder 44 limits theinsertion depth of the pin 26.

The pin 26 may also have a head portion 46 that is adjacent to a neckportion 48. The head portion 46 captures the spring clip 32. Thedistance D between the stud portion 42 and the head portion 46 is one ofthe dimensions which define the amount of deflection of the spring clip32. The tolerance of dimension D is typically a small value to controlthe clip deflection and the pull force on the thermal element 24.

Referring to FIG. 1, the cartridge 10 may further have a cover 50 thatis attached to the thermal element 24 by second pins 52 that extendthrough holes 53 in the substrate 14. The cover 50 and thermal element24 may essentially enclose the integrated circuit packages 12.

FIG. 4 shows an embodiment of a second pin 52. The pin 52 may include astud portion 54 that extends from a shoulder 56. A plastic bushing 58may be pressed onto the stud portion 54 and pressed into the thermalelement 24. The shoulder 56 limits the insertion depth of the pin 52.

The cartridge 10 can be assembled by merely sliding the pins 26 throughthe substrate 14 and snapping the spring clips 32 onto the pins 26. Thethermal grease 40 can be applied to the thermal element 24 and/or metallid 20 before the pins 26 are inserted through the substrate 14. Thecover 50 can then be snapped onto the pins 52. The cartridge does notrequire tools and is relatively easy to assemble in a manufacturingproduction line.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art. For example, as shown inFIG. 5, the thermal element 24 may be coupled directly to the integratedcircuit 18 without a metal lid. With such a configuration the integratedcircuit 18 is typically attached to a package substrate 60 with aprocess which is known as C4.

What is claimed is:
 1. An electronic cartridge, comprising: a substrate;an integrated circuit mounted to said substrate; a thermal elementadjacent to said integrated circuit; a pin that extends from saidthermal element and through said substrate; and, a spring clip attachedto said pin of said thermal element.
 2. The cartridge as recited inclaim 1, wherein said spring clip has a bent portion which exerts aforce that pulls said thermal element toward said integrated circuit. 3.The cartridge as recited in claim 1, wherein said pin is insertedthrough a slot of said spring clip.
 4. The cartridge as recited in claim3, wherein said pin has a head portion and a groove that capture saidspring clip.
 5. The cartridge as recited in claim 1, further comprisinga thermal grease located between said thermal element and saidintegrated circuit.
 6. The cartridge as recited in claim 1, wherein saidpin has a stud portion that extends from a shoulder of said pin, saidstud portion being inserted into said thermal element.
 7. A fastener toassemble an electronic cartridge, comprising: a shoulder to limitinsertion of said fastener into a thermal plate, a stud portion thatextends from said shoulder on a first side, a neck portion that extendsfrom said shoulder on a second side opposite said first side, a headportion at an end of said neck portion on said second side, said neckportion having a groove on said second side near said head portion, saidgroove to engage a spring clip such that said fastener is prevented frombeing pulled out there from, and said stud portion to couple into anopening in a thermal plate.
 8. The fastener as recited in claim 7,further comprising: a plastic bushing attached to said stud portion,said stud portion and said plastic bushing to be pressed into an openingin a thermal plate.
 9. The fastener as recited in claim 7 wherein, saidhead portion of said fastener to engage a slot of a spring clip.
 10. Thefastener as recited in claim 7 wherein, said groove to receive a pair ofopposing edges of a spring clip.
 11. The fastener as recited in claim 7wherein, the fastener to couple to a thermal plate at one end, extendthrough a substrate, and couple to a spring clip at an opposite end. 12.The fastener as recited claim 7 wherein, said stud portion includesthreads suitable to screw said fastener into an opening in a thermalplate.
 13. An electronic cartridge, comprising: a substrate having anupper and a lower edge, the substrate having a first plurality of holessituated along the upper and lower edges of the substrate; an integratedcircuit package mounted to the substrate; a thermal element adjacent tothe integrated circuit package, the thermal element having a pluralityof holes, at least two of the plurality of holes in the thermal elementcorresponding to at least two of the first plurality of holes situatedalong the upper and lower edges of the substrate; a plurality of firstpins having a first and second end, the second end having a plurality ofthreads, the plurality of first pins having the second end screwed intothe plurality of holes of the thermal element and the first end insertedthrough a second plurality of holes of the substrate; and, a pair ofspring clips attached to the plurality of first pins near the first endto hold the thermal element pressed against the integrated circuitpackage.
 14. The electronic cartridge of claim 13, wherein, the pair ofspring clips each have bent portions located at opposing edges of eachwhich are deflected such that the pair of spring clips exert a pullforce which pulls the thermal element into the integrated circuitpackage.
 15. The electronic cartridge of claim 13, wherein, the pair ofspring clips each have a pair of slots, each slot respectively engagedinto a groove located on a neck portion of each of the plurality offirst pins near the first end.
 16. The electronic cartridge of claim 15,wherein, each slot has opposing edges residing in the groove of each ofthe plurality of first pins near the first end.
 17. The electroniccartridge of claim 13, wherein, the substrat Contains a plurality ofconductive pads, the conductive pads to be inserted into a card edgeelectrical connector.
 18. The electronic cartridge of claim 13, wherein,each of the plurality of first pins has a stud portion extending from ashoulder, the stud portion having the plurality of threads in the secondend to screw into the thermal element to a depth limited by theshoulder.
 19. The electronic cartridge of claim 13, further comprising:a heat sink that is mounted to the thermal element.
 20. The electroniccartridge of claim 13, further comprising: a cover wherein the cover andthe thermal element fully enclose the integrated circuit package. 21.The electronic cartridge of claim 20, further comprising: a plurality ofsecond pins coupled to the thermal element at a second end and coupledto the cover at a first end.
 22. The electronic cartridge of claim 21,wherein, each of the plurality of second pins includes a stud portionthat extends from a shoulder, and a plastic bushing pressed onto thestud portion and pressed into the thermal element to secure the thermalelement to the cover.
 23. The electronic cartridge of claim 22, wherein,the shoulder of each limits insertion depth of the plurality of secondpins.
 24. A method to assemble an electronic cartridge comprising:attaching an integrated circuit package to a substrate, the substratehaving an upper edge and a lower edge and a first plurality of holes;coupling a plurality of first pins to a thermal element; sliding theplurality of first pins coupled to the thermal element through the firstplurality of holes to thermally couple the thermal element to theintegrated circuit package; and snapping at least one spring clip onto apair of the plurality of first pins to secure the thermal element to thesubstrate.
 25. The method of claim 24 further comprising: prior to thesliding of the plurality of first pins, pressing plastic bushings onto astud portion of each of a plurality of second pins, coupling theplurality of second pins including the plastic bushings to the thermalelement, and sliding the plurality of second pins through a secondplurality of holes in the substrate coincident with the sliding of theplurality of first pins, and after the snapping of the at least onespring clip, snapping a cover onto the plurality of second pins.
 26. Themethod of claim 24, further comprising: prior to the sliding of theplurality of first pins into the first plurality of holes of thesubstrate, applying a thermal grease between the integrated circuitpackage and the thermal element.
 27. The method of claim 24, wherein,the plurality of first pins are pressed into the thermal element, and ashoulder of each of the plurality of first pins limits insertion depth.28. The method of claim 24, wherein, the first plurality of pins arescrewed into the thermal element, and a shoulder of each of theplurality of first pins limits insertion depth.
 29. The method of claim24, wherein, the thermal element includes an integral finned heat sink.30. The method of claim 24, further comprising: coupling a heat sink tothe thermal element.
 31. The method of claim 24, wherein, the snappingof at least one spring clip includes respectively snapping a firstspring clip onto a first pair of the plurality of first pins andsnapping a second spring clip onto a second pair of the plurality offirst pins.
 32. The method of claim 24, wherein, the snapping of the atleast one spring clip includes inserting a pair of the plurality offirst pins into a corresponding pair of slots in the at least one springclip.
 33. The method of claim 32, wherein, the snapping of at least onespring clip further includes deflecting bent portions of each of thecorresponding pair of slots in the at least one spring clip to exert apull force and reduce thermal impedance between the thermal element andthe integrated circuit package.
 34. The method of claim 24, furthercomprising: prior to the sliding of the plurality of first pins into thefirst plurality of holes in the substrate, coupling a plurality ofsecond pins to the thermal element; sliding the plurality of second pinscoupled to the thermal element through a second plurality of holes inthe substrate coincident with the sliding of the first plurality ofpins; and after snapping the at least one spring clip onto the pair ofthe plurality of first pins, snapping a cover onto the plurality ofsecond pins to secure the cover over the substrate.
 35. The method ofclaim 34, wherein, the thermal element includes an integral finned heatsink.
 36. The method of claim 34, further comprising: prior to slidingthe plurality of second pins coupled to the thermal element through thesecond plurality of holes in the substrate coincident with the slidingof the first plurality of pins, applying a thermal grease between theintegrated circuit package and the thermal element.
 37. The method ofclaim 34, wherein, the plurality of second pins are pressed into thethermal element, and a shoulder of each of the plurality of second pinslimits insertion depth.
 38. The method of claim 34, wherein, theplurality of second pins are screwed into the thermal element, and ashoulder of each of the plurality of second pins limits insertion depth.39. The method of claim 34, wherein, the snapping of at least one springclip includes respectively snapping a first spring clip onto a firstpair of the plurality of first pins and snapping a second spring cliponto a second pair of the plurality of first pins.
 40. The method ofclaim 34, wherein, the snapping of the at least one spring clip includesinserting a pair of the plurality of first pins into a correspondingpair of slots in the at least one spring clip.
 41. The method of claim40, wherein, the snapping of the at least one spring clip furtherincludes deflecting bent portions of each of the corresponding pair ofslots in the at least one spring clip to exert a pull force and reducethermal impedance between the thermal element and the integrated circuitpackage.